That is a feature RotateBrush() will always run its transformation code. It won't treat modulo 90, 180, 270 and 360 rotations as special cases and run special code. But you can easily implement this yourself and just call FlipBrush() or CopyBrush() in case of a special rotation angle...

- New: RotateBrush(), TransformBrush() as well as all other functions that rotate images now use dedicated code to handle the special cases of a rotation by 90, 180, 270, and 360 degrees to transform the image data; this is much faster and the transformation is also done in a lossless way